The long-term goal of this project is to fully characterize the mechanisms by which neutrophil serine proteases regulate the inflammatory response. We hope that information gained from these studies can be used to develop strategies to inhibit the activity of these proteases in inflammatory diseases while preserving their ability to kill invading pathogens. Over the past several years, we have learned that, more than being degradative enzymes, neutrophil serine proteases can act as specific regulators of inflammation by modulating the release of cytokines and chemokines as well as activating specific receptors. Yet, the exact mechanisms by which these proteases exert these regulatory effects are still unknown. To further characterize these regulatory mechanisms in vitro and in vivo, we propose the following aims: 1. We will define the mechanisms by which cell-surface-bound cathepsin G (CG) modulates neutrophil effector functions. Our data indicate that extracellular CG cleaves a yet-unidentified molecule (or molecules) and this proteolytic modification leads to cytoskeleton reorganization, cell spreading, and effector functions. We have identified two candidate proteins as potential substrates for CG, syndecan-4 and CD43. In this aim, we will determine whether CG directly proteolyses syndecan-4 and CD43 and whether this enzymatic modification is critical for CG-dependent neutrophil effector functions. 2. We will generate a loss-of-function mutation model for proteinase 3 (PR3) to define its role in cytokine production and its contribution to inflammation in vivo. Our preliminary data suggest that in several inflammatory models, PR3 plays an important role in the local production or processing of pro- inflammatory cytokines and chemokines. To definitively study the role of PR3 in inflammation in vivo, we propose to generate a loss-of-function mutation in PR3. We will fully characterize the PR3-deficient mice and use these mutant mice for in vitro assays and in vivo models to define the physiologic role of PR3. 3. We will generate a murine model of anti-neutrophil cytoplasmic antibody (ANCA)-mediated inflammation and determine the factors that dictate disease development. ANCAs are associated with several small vessel vasculitides, including Wegener's granulomatosis. In 90% of Wegener's, ANCAs are directed against PR3, although ANCAs specific for other serine proteases are also found. We propose to determine whether all ANCAs are potentially pathogenic. We also hypothesize that decreased expression of complement regulators in the kidney may be a determinant that influences disease severity in target organ.